As a long time user of SQL::Abstract, I have a suggestion for a cleaner solution: SQL::Interpolate. (Coming soon to a CPAN near you, but ready to use now).

use SQL::Interpolate (qw/sql_interp/);

my ($sql,@bind) = sql_interp(
    " city == ",\$city," AND (sale == 1 OR rent == 1)"
);
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It provides a very natural and flexible way to mix Perl with SQL, handling bind variables for you along the way. It does handle some special cases to make INSERTS, UPDATES and "IN" clauses especially easy (like SQL::Abstract does).

After using SQL::Abstract for a long time, I'm now cheerleading SQL::Interpolate.

Like you, I hit a wall with SQL::Abstract when trying to use nested and grouped "AND and "OR" clauses. At best it was hard to read. At worst it was impossible.